Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. The pattern of the bars and spaces encode information. Bar code may be one dimensional (e.g., UPC bar code) or two dimensional (e.g., DataMatrix bar code). Systems that read, that is, image and decode bar codes employing imaging camera systems are typically referred to as imaging-based bar code readers or bar code scanners.
Imaging-based bar code readers may be portable or stationary. A portable bar code reader is one that is adapted to be held in a user's hand and moved with respect to a target indicia, such as a target bar code, to be read, that is, imaged and decoded. Stationary bar code readers are mounted in a fixed position, for example, relative to a point-of-sales counter. The bar code reader is installed behind one or more transparent windows in a housing which may be integrated into the counter. Target objects, e.g., a product package that includes a target bar code, are presented to one of the one or more transparent windows and thereby pass within a field of view of the stationary bar code readers. The bar code reader typically provides an audible and/or visual signal to indicate the target bar code has been successfully imaged and decoded.
A typical example where a stationary imaging-based bar code reader would be utilized includes a point of sale counter/cash register where customers pay for their purchases. The reader is typically enclosed in a housing that is integral to the counter and normally includes a vertically oriented transparent presentation window and a horizontally oriented transparent presentation window, either of which may be used for reading the target bar code affixed to the target object, i.e., the product or product packaging for the product having the target bar code imprinted or affixed to it. The sales person (or customer in the case of self-service check out) sequentially presents each target object's bar code either to the vertically oriented window or the horizontally oriented window, whichever is more convenient given the specific size and shape of the target object and the position of the bar code on the target object.
A stationary imaging-based bar code reader that comprises a plurality of imaging cameras assemblies or systems is sometimes referred to as a bioptic or multicamera imaging-based scanner or bar code reader. In a multicamera imaging reader, a plurality of imaging camera assemblies are positioned within an interior region of a housing. The housing also supports a plurality of transparent, presentation windows. Fold mirrors are appropriately positioned within the housing interior region to direct a field of view of one or more camera assemblies such that an imaging or scanning volume of the camera more closely conforms to a desired imaging field, region or volume of the reader.
While the fields of view of two or more camera assemblies may overlap to some degree, the effective or total imaging region or imaging volume of the reader is increased by adding additional camera systems. Hence, by virtue of having a plurality of imaging camera assemblies and appropriately positioned fold minors in the housing interior region, a multicamera reader will generally have a multidirectional effective total imaging region compared to single camera imaging bar code reader which requires presentation of a target bar code to the reader in a very limited orientation to obtain a successful, decodable image, that is, an image of the target bar code that is decodable.
As previously mentioned, the camera systems of a multicamera imaging reader includes a plurality of imaging cameras assemblies and a plurality of fold minors disposed within the reader housing and positioned with respect to the transparent presentation windows such that when a target object is presented to the housing presentation windows for reading the target bar code on the target object, the target object is imaged by the plurality of imaging camera assemblies, each camera assembly providing a different image of the target object. For example, one camera assembly may image a top view of the target object, another camera may image a bottom view of the target object, yet another camera assembly may image a first side of the target object. Depending on the position of the camera assemblies within the housing and the size of the target object being imaged, it is possible for a small target object, e.g., a small six sided box containing a bottle of aspirin, that all six sides of the target object may be imaged. Thus, it is also clear that increasing the number of camera assemblies increases the ability to image a target bar code on a target object and provides greater flexibility as to how the target object may be oriented or presented to the housing or the transparent presentation windows while still achieving at least one decodable image.
Each camera assembly of a multicamera imaging-based bar code reader is characterized by an imaging or scanning volume, that is, a region or volume wherein if a target bar code of a given density is presented within the region, a sufficient sharp image of the target bar code will be projected onto a sensor array of the camera assembly by the imaging lens assembly such that the imaged target bar code can successfully be decoded by a decoder. Or, if the reader is used for imaging, i.e., imaging a signature, the region or volume of the camera assembly wherein, if a signature is presented within the region, a sufficiently sharp image of the signature will be projected onto the sensor array of the camera assembly by the imaging lens assembly for the desired purposes of imaging, for example, verification of the signature.
The imaging or scanning volume is determined by the characteristics of the sensor array and the imaging lens assembly. Depending on the position of the camera assembly within the housing, whether or fold mirror is used, the idea is to have the imaging or scanning volume, to as great a degree as possible, to be within the desired imaging field of the reader. It is also desired, that for all camera assemblies taken together, the effective or combined total imaging field of the reader, that is, when all scanning volumes are combined, is as close as possible to including an entirety of the desired imaging field of the reader and is multidirectional, that is, successful imaging can occur in any direction or orientation with the total imaging field of the reader.
In a multicamera imaging-based bar code reader with a horizontal presentation window and an orthogonal presentation window, it is desired to be able to read a target bar positioned adjacent either presentation window, even if the target bar code is oriented facing away from the presentation window. For example, if an object is presented to the horizontal presentation window and the target bar code is facing upwardly, that is, away from the presentation window, it will often times be the case that an effective imaging region or scanning volume of the camera assembly positioned to image a portion of a target object facing away from the presentation window is insufficient to read the target bar code. One reason for this insufficiency is that the scanning volumes of conventional camera assemblies are symmetric with respect to the optical axis of the camera imaging lens assembly, that is, a working range or depth of field of a camera assembly is limited uniformly over the field of view of the camera.
While a symmetric scanning volume may be appropriate for a camera assembly whose field of view is not intersected and directed by a fold mirror, for a camera assembly whose field of view is directed though a presentation window by the use of a fold mirror, a symmetric scanning volume may not comport with the desired imaging field of the reader. Additionally, even if the scanning volume for a particular camera assembly whose field of view is directed by a fold mirror is within the desired imaging field of the reader, the scanning volume for that camera assembly may be less than optimal. For example, there may be a peripheral portion or region of the desired imaging field which is not covered by the fields of view of any other camera assemblies of the reader. It would be desired to have the particular camera assembly cover that peripheral portion of the desired imaging field. However, because of the symmetric scanning volume of the camera assembly, it cannot cover the peripheral portion of the desired imaging field.
What is needed is a multicamera imaging-based bar code reader wherein the scanning volumes of individual camera assemblies are optimized to provide an effective or combined total imaging field or volume of the camera assemblies to more closely comport to a desired imaging field or volume of the reader. What is also needed is a multicamera imaging-based bar code reader with the ability to read target bar codes positioned adjacent to, but facing away from either the horizontal or vertical presentation windows.